#!/usr/bin/evn python3
# -*- coding: utf-8 -*-

# ---------------------------------------------------------------------------------------------------
# DOM vs SAX
"""
XML虽然比JSON复杂，在Web中应用也不如以前多了，不过仍有很多地方在用，所以，有必要了解如何操作XML。
操作XML有两种方法：DOM和SAX。

DOM会把整个XML读入内存，解析为树，因此占用内存大，解析慢，优点是可以任意遍历树的节点。

SAX是流模式，边读边解析，占用内存小，解析快，缺点是我们需要自己处理事件。

正常情况下，优先考虑SAX，因为DOM实在太占内存。

在Python中使用SAX解析XML非常简洁，通常我们关心的事件是
start_element，end_element和char_data，准备好这3个函数，然后就可以解析xml了。

举个例子，当SAX解析器读到一个节点时：
<a href="/">python</a>

会产生3个事件：
    1.start_element事件，在读取<a href="/">时；

    2.char_data事件，在读取python时；

    3.end_element事件，在读取</a>时。

用代码实验一下：
"""
from xml.parsers.expat import ParserCreate

class DefaultSaxHandler(object):
    def start_element(self, name, attrs):
        print('sax:start_element: %s, attrs: %s' % (name, str(attrs)))

    def end_element(self, name):
        print('sax:end_element: %s' % name)

    def char_data(self, text):
        print('sax:char_data: %s' % text)

xml = r'''<?xml version="1.0"?>
<ol>
    <li><a href="/python">Python</a></li>
    <li><a href="/ruby">Ruby</a></li>
</ol>
'''

handler = DefaultSaxHandler()
parser = ParserCreate()
parser.StartElementHandler = handler.start_element
parser.EndElementHandler = handler.end_element
parser.CharacterDataHandler = handler.char_data
parser.Parse(xml)


"""
需要注意的是读取一大段字符串时，CharacterDataHandler可能被多次调用，
所以需要自己保存起来，在EndElementHandler里面再合并。

除了解析XML外，如何生成XML呢？99%的情况下需要生成的XML结构都是非常简单的，
因此，最简单也是最有效的生成XML的方法是拼接字符串：

"""
L = []
L.append(r'<?xml version="1.0"?>')
L.append(r'<root>')
#L.append(encode('some & data'))    #'some & data'.encode()
L.append('some & data')
L.append(r'</root>')
#return ''.join(L)
print(''.join(L))
print('\n')

"""
如果要生成复杂的XML呢？建议你不要用XML，改成JSON。
小结

解析XML时，注意找出自己感兴趣的节点，响应事件时，把节点数据保存起来。解析完毕后，就可以处理数据。

练习

请利用SAX编写程序解析Yahoo的XML格式的天气预报，获取当天和第二天的天气：

http://weather.yahooapis.com/forecastrss?u=c&w=2151330

参数w是城市代码，要查询某个城市代码，可以在weather.yahoo.com搜索城市，浏览器地址栏的URL就包含城市代码。
"""
from xml.parsers.expat import ParserCreate
class WeatherSaxHandler(object):
    def __init__(self):
        self.List = {}
        self.count = 0
        
    def start_element(self, name, attrs):
        if name == 'yweather:location':
            self.List['city'] = attrs['city']
            self.List['country'] = attrs['country']
            #print('List: %s' % str(self.List))
            
        if  name == 'yweather:forecast':
            self.count+=1
            # {'day': 'Wed', 'date': '27 May 2015', 'low': '20', 'high': '33', 'text': 'Partly Cloudy', 'code': '30'}
            if self.count == 1:
                self.List['today'] = attrs
                self.List['today']['low'] = int(self.List['today']['low'])
                self.List['today']['high'] = int(self.List['today']['high'])
                #print("List['today']['low']: %s" % str(self.List['today']['low']))
            if self.count == 2:
                self.List['tomorrow'] = attrs
                self.List['tomorrow']['low'] = int(self.List['tomorrow']['low'])
                self.List['tomorrow']['high'] = int(self.List['tomorrow']['high'])
                #print("List['tomorrow']: %s" % str(self.List['tomorrow']))
            
    def end_element(self, name):
        pass

    def char_data(self, text):
        #print('sax:char_data: %s' % text)
        pass


        
def parse_weather(xml):
    L = {}
    handler = WeatherSaxHandler()
    parser = ParserCreate()
    parser.StartElementHandler = handler.start_element
    parser.EndElementHandler = handler.end_element
    parser.CharacterDataHandler = handler.char_data
    parser.Parse(xml)
    
    return handler.List

# 测试:
data = r'''<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
<rss version="2.0" xmlns:yweather="http://xml.weather.yahoo.com/ns/rss/1.0" xmlns:geo="http://www.w3.org/2003/01/geo/wgs84_pos#">
    <channel>
        <title>Yahoo! Weather - Beijing, CN</title>
        <lastBuildDate>Wed, 27 May 2015 11:00 am CST</lastBuildDate>
        <yweather:location city="Beijing" region="" country="China"/>
        <yweather:units temperature="C" distance="km" pressure="mb" speed="km/h"/>
        <yweather:wind chill="28" direction="180" speed="14.48" />
        <yweather:atmosphere humidity="53" visibility="2.61" pressure="1006.1" rising="0" />
        <yweather:astronomy sunrise="4:51 am" sunset="7:32 pm"/>
        <item>
            <geo:lat>39.91</geo:lat>
            <geo:long>116.39</geo:long>
            <pubDate>Wed, 27 May 2015 11:00 am CST</pubDate>
            <yweather:condition text="Haze" code="21" temp="28" date="Wed, 27 May 2015 11:00 am CST" />
            <yweather:forecast day="Wed" date="27 May 2015" low="20" high="33" text="Partly Cloudy" code="30" />
            <yweather:forecast day="Thu" date="28 May 2015" low="21" high="34" text="Sunny" code="32" />
            <yweather:forecast day="Fri" date="29 May 2015" low="18" high="25" text="AM Showers" code="39" />
            <yweather:forecast day="Sat" date="30 May 2015" low="18" high="32" text="Sunny" code="32" />
            <yweather:forecast day="Sun" date="31 May 2015" low="20" high="37" text="Sunny" code="32" />
        </item>
    </channel>
</rss>
'''
weather = parse_weather(data)
assert weather['city'] == 'Beijing', weather['city']
assert weather['country'] == 'China', weather['country']
assert weather['today']['text'] == 'Partly Cloudy', weather['today']['text']
assert weather['today']['low'] == 20, weather['today']['low']
assert weather['today']['high'] == 33, weather['today']['high']
assert weather['tomorrow']['text'] == 'Sunny', weather['tomorrow']['text']
assert weather['tomorrow']['low'] == 21, weather['tomorrow']['low']
assert weather['tomorrow']['high'] == 34, weather['tomorrow']['high']
print('Weather:', str(weather))




